linux-kernel - Re: [PATCH v3 2/3] clocksource: Add NPS400 timers driver

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Date:	Tue, 9 Feb 2016 23:55:13 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Noam Camus <noamc@...hip.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>,
	"marc.zyngier@....com" <marc.zyngier@....com>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Tal Zilcer <talz@...hip.com>,
	Gilad Ben Yossef <giladb@...hip.com>,
	Rob Herring <robh+dt@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH v3 2/3] clocksource: Add NPS400 timers driver

On 02/09/2016 10:47 PM, Noam Camus wrote:
>> From: Daniel Lezcano <daniel.lezcano@...aro.org> Sent: Tuesday,
>> February 9, 2016 3:38 PM
>
>> Actually I was referring to clk_prepare_enable,
>> clocksource_register_hz. Agree clk_get_rate is always valid.
> Thanks for making this clear. Any way as you can see I do call
> pr_err() in case of error just like most drivers around. By "hang" do
> you mean calling panic()?

No. I meant the errors are caught but no action is taken, the execution
continues normally as nothing wrong happened. This is why I asked if you
expect the host to hang at boot time with the last error as a hint.

I was expecting to see a call to clk_disable_unprepare if
clocksource_register_hz fails, and returning 'ret' if clk_prepare_enable
fails.

> What if there is another clocksource in DT (even with worse rating)?
> I still prefer using it then having non workable machine.

You are right. This is why failing gracefully in the init function is
important.

>>>> You can simplify the driver even more by using
>>>> clocksource_mmio_init.
>>> Since my base address depends on cluster number, which CPU is
>>> part of,  this interface is not much of a use. On top of that it
>>> assumes that I am little endian by using readl family
>>> accessories.
>
>> Why can't you use ?
>
>> clocksource_mmio_init(nps_msu_reg_low_addr, "EZnps-tick",
>> nps_timer_rate, 32, nps_clksrc_read);
>
> I believe that the simplification is meant for drivers that can
> actually use the clocksource_mmio..() accessories. Could you explain
> what is the advantage here, for my case, to use clocksource_mmio
> driver?

Using the mmio generic code will save:

+static struct clocksource nps_counter = {
+	.name	= "EZnps-tick",
+	.rating = 301,
+	.read   = nps_clksrc_read,
+	.mask   = CLOCKSOURCE_MASK(32),
+	.flags  = CLOCK_SOURCE_IS_CONTINUOUS,
+};

Up to you.

   -- Daniel

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